In a randomized, controlled study, ribavirin small-particle aerosol was found to be effective in the treatment of influenza B virus infection in a group of college students. Eleven treated patients experienced significantly more rapid defervescence, disappearance of systemic illness, and reduction of virus shedding in nasal secretions than ten control patients treated with a saline aerosol. Antibody response to infection was similar in both groups. The treatment was well tolerated, and hematologic and clinical chemical tests demonstrated no toxicity. The estimated dose of ribavirin aerosol retained was about 2 g in 39 hours of treatment during the first 60 hours in the hospital.